Phosphate Homeostasis Flashcards
Role of phosphate in physiology
Bone mineral - calcium hydroxyapatite Ca10(PO4)6(OH)2
Nuclei acids
Phospholipids
ATP
cAMP
Post-translational modification of proteins
Amount of whole body phosphate
500-800g
1% total body weight
Serum phosphate amount
0.8-1.5 mmol/L
What percentage of phosphate is found in bone mineral
90%
Low phosphate
Poor bone mineralisation
-rickets or osteomalacia
-pain and fractures
High phosphate
Excessive formation of hydroxyapatite
Deposition in tissues other than bone
Dietary sources of phosphate
Protein:
Animal
Dairy
Soy
Seeds
Nuts
Recommended daily intake of phosphate
700 mg
What percentage of phosphate is reabsorbed in PCT of kidney
80%
Renal phosphate handling
Maximum rate of reabsorption is limited
So excess is excreted
How is phosphate reabsorbed in PCT
Na co-transporter
How much phosphate is filtered in the glomerulus
90%
How much phosphate is reabsorbed in the DCT
10%
What hormones regulate phosphate
Parathyroid hormone
1,25 dihydroxyvitamin D
FGF-23
Effect of parathyroid hormone on phosphate
Increases 1,25 vitamin D so increases active gut absorption
Decreases tubular reabsorption of phosphate- increases renal excretion
FGF-23
Fibroblast growth factor 23
What is the major regulator of phosphate metabolism,
FGF-23 (fibroblast growth factor 23)
Where is FGF-23 produced
Osteocytes
What stimulates the production of FGF-23
Rise in phosphate levels
Dietary phosphate loading
Parathyroid hormone
1,25 vitamin D
Actions of FGF-23
Decreases expression of Na transporter in renal tubule- increases renal excretion
Decreases 1 alpha-hydroxylation of vitamin D- decrease gut absorption
Decreases whole body phosphate
Secondary regulator of phosphate
Parathyroid hormone
How is phosphate found in serum
50% free ions
35% complexed
10% protein bound
What does phosphate complex with in blood serum
Na+
Ca2+
Mg2+
What percentage of ingested phosphate is absorbed
70-80%
